There are plenty of great slow burn horror movies.
This is definitely not one of them.
I'll start with the good. Parents are clearly trying their best to carry the film, Dermot Mulroney and Leslie Bibb. The main actress is ok, which may be more of an indictment of the writing than the actress herself, since I thought she was good in Hellraiser. Practicals are good, but they use so many damn quick cuts they are normally wasted.
Everything else is pretty bad: we have the cinematography trope of "person is going crazy here's some quick cuts of blood", characters with odd motivations that don't make sense, subplots that are damn near irrelevant or exist to serve as red herrings.
By the end of the climax of the film I just couldn't care less what type of twist was coming.
This seemed like a pretty boiler plate slasher that tried and failed to be something more.